1. Field of the Invention
This invention relates to a method and apparatus for detecting a defect formed at an intersection part of a united part of an object to be measured which has two plate parts having one section with the plate surfaces opposite to each other and other section that is united integrally with said one section or is bonded to said one section with the other section having the intersection part to said plate part, such as a turbine blade used in a turbine engine.
Further, this invention also-relates to a method and apparatus capable of detection of a change in thickness of two plate parts due to a change in the state of plate surfaces of the two plates sections of an object to be measured, such as a turbine blade, which has a section with the plate surfaces of the two plate parts opposite to each other with a gap between them, such as a turbine blade used in a turbine engine mentioned above.
Further, this invention relates to a method and apparatus for predicting the life of an object to be measured by detecting the degree of deterioration of a section of the object to be used that is mainly used thereby enabling the life of the particular object to be measured to be predicted.
2. Description of the Prior Art
If a structure, such as a machine and a part of a product, has a defect, such as a crack, a cavity called "su" in Japanese, or a recess, there is a risk that leads to various inconveniences, and therefore it is desired that the part having a defect, such as a crack, a cavity, and a recess, is eliminated by detecting the presence of such a defect in advance.
Heretofore, as means of detecting a crack or the like, nondestructive inspection methods are known. Nondestructive inspection methods that are now available include, for example, an ultrasonic wave reflection method of detecting defects by using ultrasonic waves reflected, a so-called AE (acoustic emission) detection method based on sounds attributable to the formation of a crack, an observation method using a CCD camera, an X-ray photograph method, and a color check method.
Meanwhile, with respect to structures, such as parts, there are many structures that have a part in the shape with two platelike items bonded together (including the case wherein two platelike items are integrally constructed) in order to make it light or to provide the inside thereof with a flow passage for a gas or a liquid.
For instance, the blade part of a turbine blade of a turbine engine of an airplane has a structure that two opposite platelike items with a gap between them are connected through bridge sections. The spaces partitioned by the bridge sections are constructed to serve as flow passages for heated air.
The turbine blade is composed of blade parts, a pedestal that is called a so-called platform part and to which the blade parts are connected, and a leg part continuous to the pedestal.
In the case of such a structure, the pedestal that is a united section joining the blade part to the leg part is in a state having an intersection part with surfaces intersecting at a prescribed angle, for example, 90.degree., like an L-shaped part. In this specification, the term "unite" include both "connect different sections" and "unite integrally different sections".
In such an intersection part wherein surfaces intersect like an L-shaped part, stress is concentrated in many cases, and such a section is apt to be scared. Further, in the case wherein a scar of the intersection part has penetrated into the part of the joined section, the scar in concert with the concentration of stress into the intersection part is enlarged, which will likely lead to destruction or the like of the united part, and therefore it is desirable that a scar in the intersection part can be detected separately from other sections.
However, in the case wherein a scar formed in said intersection part is probed by the above-described conventional nondestructive inspection method, it is required to probe this intersection part in a concentrated manner. In the case wherein the examination is carried out in such a manner, the ultrasonic reflection method of examining a defect is a contact method and measures only the section where a sensor is applied because of rectilinear propagation of ultrasonic waves, and therefore there are such disadvantages that the examination takes time, and judgement is not easy because of reflection of ultrasonic waves due to nonalignment in the sensor connection surface and because visible waveforms become different depending on a small angular difference of the propagation direction of ultrasonic waves.
Further, in the case of the AE method, it is a contact method like the ultrasonic reflection method of examining a defect and there is the problem that the measurement is impossible if the crack is not a linear crack. In addition, in some cases of linear cracks, it is required to carry out the measurement with the crack being increased.
Further, in the case of the observation method using a CCD camera, there is the fault that a judgement is disturbed if there is a stain or a pattern other than a crack. Further, in the case of the X-ray photograph method, although it is effective because a direct visual observation is possible, for example, there is the fault that the amount of X-ray is required to be adjusted depending on the thickness of the object to be measured and this adjustment is troublesome not to allow observation.
A first object of this invention is to provide a method and apparatus for detecting a defect that is capable of detecting quickly and easily a defect, such as a crack and a cavity, formed in an intersection part of a structure as described above without causing faults as mentioned above.
By the way, since hot air is passed through the inside of a blade part of a turbine blade, the inner wall surface thereof is oxidized. Then with the passage of the operating time, a crack and the like are formed in the oxidized section, the particular inner wall surface section comes off, and the platelike item constituting the blade part becomes thinner. Therefore, it is important to monitor the thickness of the platelike item constituting the blade part to judge the deterioration of the turbine blade or to judge the necessity of the repair.
However, if a change in the thickness of this blade part is measured by the above-mentioned conventional nondestructive inspection method, generally it takes very long time, and in some cases, even it requires to take 1 hour to measure a thickness. Further, most of the conventional nondestructive inspection methods are contact-type inspection methods wherein measurement is carried out with a sensor in contact with a site to be-checked, and therefore are not suitable, for example, for judgement of a defect in the blade part.
A second object of this invention is to provide a method and apparatus that can detect quickly and easily a defect formed in the inner surface of a section which is possessed by an object to be measured and wherein two plate parts are opposed with a prescribed gap between their plate surfaces as described above and a change in thickness of the plate parts of that particular section resulted thereby.
Further, the conventional methods of detecting a defect as described above detect whether or not a defect or the like is formed in an object to be measured and are not suitable for knowing the life of an object to be measured as to ascertain how long the object to be measured can be used safely.
However, parts are gradually deteriorated by the use thereof and, for example, in the case of turbine blades used in turbine engines of airplanes described above, it is very important to predict the life thereof and prevent a serious accident from occurring by replacing it in a suitable early stage before the formation of a defect or the like.
In that case, the blade part in the turbine blade is deteriorated mainly by the use thereof and it is expected that the progress of deterioration is quicker in the blade part than in the pedestal called the platform part to which the blade part is united. Therefore it is important to detect the degree of deterioration of the blade part.
A third object of this invention is to provide a method and apparatus that can predict the life of an object to be measured that has a first section which is a major working section and a second section that is united integrally with said first section or is bonded to said first section by detecting the degree of deterioration of said first section.